Mineral material, such as stone, is retrieved to be crushed from the ground either by exploding or by digging. The mineral material may also comprise natural stone, gravel and construction waste. Both mobile crushers and fixed crusher applications are used for crushing. The material to be crushed is fed with an excavator or a wheel loader into a feed hopper of the crusher, from where the material to be crushed falls into the jaws of the crusher, or a feeder or a feeder device transfers the stone material towards the crusher.
A mineral material processing plant comprises one or more crushers and/or screens and possibly further devices such as conveyors. The processing plant may be fixed or mobile. In particular mobile processing plants are used in urban surroundings in processing recyclable material such as construction waste.
Preferably a mineral material processing plant is operated with full capacity, i.e. the amount of mineral material processed is kept as high as possible but within safety and other limits of the equipment used. This requires that the process parameters, such as the homogeneity and type of material to be crushed are suitable. Typically a crusher has an upper limit for a value, such as pressure, representing the load and stresses in the crushing chamber.
From patent publication U.S. Pat. No. 8,540,175 a method is known in which a stress reference value is set. A statistical value representing peak stress is calculated from average stress and standard deviation thereof. If this value exceeds the stress reference value, the crusher is controlled in order to reduce the stress and vice versa. In other words, a “safety margin” calculated from standard deviation is added to average stress value, and the resulting value is kept under the stress limit.
The above method shows little consideration for the effect of the stress profile on the crushing process, but merely considers a statistical peak value that has to be kept under a limit. Accordingly, an objective of the invention is to provide a method for controlling a mineral material processing plant that considers the stress profile on a given operating situation and provides efficient usage of the full capacity of the processing plant.